1. Field of the Invention
The present invention belongs to a technical field of an image processor for correcting degradation in image quality due to a photographic lens, which occurs in an image photographed by a film-with-lens camera, a low-price compact camera, a digital camera, and the like, so as to obtain a high-quality image.
2. Description of the Related Art
Conventionally, so-called direct exposure for projecting an image on a film onto a photosensitive material (photographic paper) and then performing plane exposure on the photosensitive material is a main technique in printing of an image photographed on a photographic film (hereinafter, referred to simply as a film) such as a negative film or a reversal film onto a photosensitive material.
On the other hand, a printer utilizing digital exposure, that is, a digital photographic printer has recently been put into practical use. In the digital photographic printer, an image recorded on a film is photoelectrically read out. The readout image is converted to a digital signal, which is then subjected to various image processings so as to obtain image data for recording. A photosensitive material is subjected to scanning exposure with recording light which is modulated in accordance with the obtained image data so as to record an image (latent image), thereby obtaining a (finished) print
The digital photographic printer basically includes: an image input device having a scanner (image reader) for photoelectrically reading out an image recorded on a film and an image processor for performing image processing on the readout image so as to convert it to image data for output (exposure condition); and an image output device having a printer (image recorder) for performing scanning exposure on a photosensitive material in accordance with the image data output from the image input device so as to record a latent image and a processor (developing unit) for performing a developing processing on the exposed photosensitive material so as to obtain a print.
In the scanner, reading light emitted from a light source is irradiated onto a film so as to obtain projected light bearing an image photographed on a film. The projected light forms an image through an imaging lens on an image sensor such as a CCD sensor, which is photoelectrically converted so as to read out the image. After performing various processings as the need arises, the readout image is sent to an image processor as image data of the film (image data signal).
The image processor sets an image processing condition from the image data read out by the scanner, and performs the image processing on the image data in accordance with the set condition so as to send the obtained data to a printer as output image data (exposure condition) for image recording.
In a printer, for example, in the case of the one utilizing light beam scanning exposure, a light beam is modulated in accordance with image data sent from the image processor. The modulated light beam is deflected in a main scanning direction while a photosensitive material is being conveyed in a sub-scanning direction perpendicular to the main scanning direction so as to expose (print) the photosensitive material with the light beam bearing the image, thereby forming a latent image. Then, developing processing or the like in accordance with the photosensitive material is performed in the processor so as to obtain a print (photograph) on which the image photographed on the film is reproduced.
In the digital photographic printer, an image can be converted into digital image data, so that an exposure condition upon printing is determined by image data processing. Therefore, the correction for washed-out highlights or flat shadows of an image due to backlight, flash photograph and the like, the sharpness processing (sharpening), the correction for color or density failure and the like are suitably performed so as to obtain a high-quality print which cannot be obtained with conventional direct exposure.
On the other hand, a large amount of low-price handy film-with-lens cameras, compact cameras and the like have been recently shipped. In these low-price film-with-lens cameras and compact cameras, due to cost limit, so-called one-element lens or two-element lens is used to reduce the cost of lens. As a result, there arises a problem in that a photographed image is degraded due to aberrations of a lens such as deterioration of marginal luminosity, lateral chromatic aberration and distortion aberration resulting from lens performance.
As described above, however, since various processes can be performed on input image data by means of digital image data processing in the digital photographic printer, the degradation in image quality due to these types of lens aberration can be corrected to improve the image quality. Various correction methods for a degraded image have been conventionally proposed as described below.
For example, JP 6-237376 A discloses a deteriorated picture recovery system for recording picture quality deterioration information specific to each camera to a laboratory side and selecting the deterioration information based on an identification code of a camera used for the image pickup to recover the photographed deteriorated picture.
JP 9-281613 A discloses a technique for searching an image quality correction information table which is recorded in advance on a laboratory side based on camera type identification information, film kind identification information and photographing time information recorded on a negative film so as to fetch information for correcting image quality deterioration of an image to correct image data, thereby obtaining a high-quality photographic print.
Furthermore, JP 11-225270 A discloses an image processing method for correcting at least one of lateral chromatic aberration, distortion aberration, marginal luminosity, and an image blur from characteristics of a lens used for photographing an image and from positional information of the image so as to output a high-quality image whose image quality deterioration is corrected by image processing, even if the image is photographed with a film-with-lens camera or the like.
As described above, the image deterioration correction by means of digital image processing fairly improves the quality of an image photographed even with a film-with-lens camera and the like. However, an inconvenience occurs in image quality after performing correction processing, depending on a combination of these image deterioration correction processings and other image processings. For example, in the case where the soft focus processing is followed by the marginal luminosity correction, an inconvenience sometimes occurs in an output image, such as the occurrence of pseudo contours. Thus, there is a room to further improve the conventional attempts of improving image quality.